MAC Address on an ASIX ax88796 chip question

troubleshooting asix ax88796

Hello,

I've a question and i hope that someone can help me with it.

What are the requirements of a MAC address? I've found some problems when using different MAC addresses.

It seems that not every address is a valid one. And if so, my asix only accepts broadcasts.

When I'm using the MAC address: [ 'O', 'F', 'F', 'I', 'C', 'E' ] i only receive broadcasts. (I've seen this example in a book.)

But when i'm using the example of Fred Eady [ 0, 0, 'E', 'D', 'T', 'P' ] it works fine.

Does a MAC address has to start with a zero? or two?

I'm waiting for registered MAC addresses, but i'm asking this question just because this problems took al lot of time..


Thnx alot.

asix ax88796 chip

Hi,

There are 3 types of MAC Address:-

UNICAST
MULTICAST
BROADCAST

A Broadcast is signified by the address FF:FF:FF:FF:FF:FF and every device attached to the segment is required to process it.
A Multicast MAC Address contains a 1 in bit position 0 of the 1st byte of the address.
A Unicast MAC Address contains a 0 in bit position 0 of the 1st byte of the address.
Bit 1 of the first byte contains a flag which specifies if the MAC Address is Globally Unique (0) or whether it is Locally Administered (1).

If it is Globally Unique then you need to register with the IEEE, they will then assign you values for the first three bytes of the MAC Address which no-one else is allowed to use (hence, Globally Unique).

Most people choose not to Locally Administer their MAC Addresses due to the fact that you have to come up with your own numbering scheme to prevent duplicate MAC Addresses on your LAN - invariably mistakes are made and you spend an afternoon troubleshooting the network )

There is a page on Wikipedia which shows the make up of a MAC Address:-

https://en.wikipedia.org/wiki/MAC_address

Hope this helps.

Cheers,
Adrian.